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THE ART OF GALVANIZING 



By Alfred Sang, Pittsburg. Pa. 



One of the most persistent problems 
which confront the worker in iron and 
steel is the prevention of corrosion. We 
cannot rid ourselves of the agents which 
effect the corrosion of iron without at 
the same time ridding ourselves of the 
agents which are essential to life itself. 
Air is indispensable both to human res- 
piration and for the formation of rust 
and other oxides for which it supplies 
the oxygen ; moisture is necessary for 
the formation of clouds which make the 
earth fertile, and it also supplies the 
medium in which rusting takes place 
and hydrates the oxide; carbonic diox- 
ide is an animal by-product, and a raw 
material for the vegetable world, and 
the exchange of carbonic dioxide and 
oxygen, which is continually taking 
place between the animal and vegetable 
kingdoms is of vital importance; then, 
on the other hand, rust is not readily- 
formed — if at all — unless there be an 
acid present, and the acid which is most 
universally distributed is carbonic acid 
or hydrated carbonic dioxide. There is, 
as you see, a close relationship between 
the processes of living and rusting, but 
while human beings make up for the 
rusting or decaying of their tissues by 
nutrition, it has not yet been discovered 
how to feed or regenerate iron, and un- 
til such a discovery is made we are com- 
pelled to take our cue from the ancient 
Egyptians and resort to embalming. 
Methods for Protecting Iron and Steel. 

There are two general ways of em- 
balming iron to prevent its decomposi- 
tion, which might be called respectively 
the non-metallic and metallic methods. 
In the non-metallic method, the articles 
are coated with an organic substance, 
usually oil or varnish, the efficiency of 
which depends on its being more or less 
air tight; when coloring matter is add- 
ed to the oil it becomes a paint, but I 
understand from authorities on the sub- 
ject that a varnish free from pigments 
is preferable to anything else. The 
metallic method consists in coating the 



iron with some other metal, and it , 
this method which I have come to discuss 
with you. 

The Composite Nature of Steel. 

Iron rusts less readily than does steel; 
this is perhaps due to steel being a very 
composite material. In the iron, which 
forms the bulk of its composition, are 
dissolved or immersed a great variety 
of other substances; some of these are 
simple, such as graphite, silicon and 
manganese, and others are compound, 
such as carbides, sulphides, phosphides 
and silicides; the carbon compounds are 
very numerous and diversified, being due 
to different heat treatments; the best 
known are cementite, pearlite and mar- 
tensite. Just as variety is, to some 
people, the spice of living, so is hetero- 
geneous composition the spice of rusting, 
in the present instance at any rate; nor 
is this by any means a solitary instance; 
it is a well £nown fact that chemically 
pure zinc is dissolved very slowly by cer- 
tain acids, whereas the commercial prod- 
uct, especially if it be high in iron, is 
rapidly dissolved.* 

When -"'steel is attacked by an acid 
pickle its surface is due to the iron dis- 
solving first* and the impurities be- 
ing left ai a poorly adhering black 
powder. For some work which has 
to be coated, and especially if the 
coating is non-metallic, it is desirable 
to remove the surface "rottenness'' by 
means of the sand-blast; the sand-blast 
is often inconvenient or undesirable, but 
a high pressure water jet is also ef- 
fective and will remove at the same 
time the gelatinous or colloidal salts of 
iron which are left on the surface of 
the steel. 

Metallic Coatings. 

If the metallic coating is considered 
merely as a garment which protects the 



* The theory has been advanced by Weeren 
that this passiveness of pure zinc is due to 
the formation of a condensed layer of hydro- 
gen on the surface, which prevents further 
action of the acid. It is difficult to see how 
the presence of iron would prevent the ac- 
cumulation of hydrogen. 



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TRAN^4CTT KS AMERICAN FOUNDRYMEN'S ASSOCIATION 



/ 



iron article i^" atmospheric influences, 
the point3^P" cn ™ust receive special 
consider;]** 3 ' 11 are tne closeness of the fit 
and th/- irnpenetralile qualities of the 
coa tins'- A close fit is more readily ob- 
tain/" by depositing the metals electric- 
, ;/?. In hot processes the uneven con- 
fraction of the coating and coated met- 
als — the latter usually having the lower 
coefficient — will cause blisters which are 
not always noticeable to the naked eye 
but which are none the less present. 
This poor adherence due to uneven con- 
traction is evidenced by the flaking 
which will take place when the articles 
arc bent; with articles which do not 
undergo bending, such as castings, there 
may not be any flaking, but the air 
spaces are there just the same and oxi- 
dation will take place under the blisters, 
out of sight, slowly but surely, if the air 
is given access. Unfortunately the air 
has free access to these spaces because 
no hot coated surface which has not re- 
ceived a mechanical treatment in the hot 
state, such as rolling, is free from faults 
and crevices: especially is this the case 
in rough and irregular work like cast- 
ings where the variety of strains taking 
place at the moment of setting of the 
coating metal produce an equivalent va- 
riety of microscopical fissures. Through 
these fissures the air, moisture and car- 
bonic dioxide have free access to the 
iron. 

An electrically deposited coating ad- 
heres a great deal better than does a 
hot coating, and this is the greatest 
point in its favor ; unfortunately, it is 
almost impossible to obtain a sur- 
face free from pores. Every pho- 
tographer knows how specks of dust 
will cause pinholes in his negatives: a 
particle of dust is more or less light- 
proof and protects the point of the film 
on which it rests from the chemical ac- 
tion of light In electrolytic work each 
speck of impurity prevents the metal-ions 
of the electrolyte from depositing on the 
spot covered by the impurity and a pin- 
bole or pore is the result. These pin- 
holes are like weds with a spot of rust, 
a -speck of dirt or a particle of oil at the 
bottom, each of which is sufficient in 
itself to prevent the deposition of the 
coating metal, but none of which is able 



to prevent the access of the corroding 
agencies. Under the microscope rust 
will be found to originate in all cases in 
the pores, and I have examined speci- 
mens where the rust seemed to fairly 
ooze out of them. If articles could be 
made perfectly clean before being coated, 
the electrolytic process would be perfect 
as regards the two points of quality re- 
quired of a coating considered as a cov- 
ering only. 

The Coating as a Mechanical 
Protection. 
Considered merely as a mechanical 
protection, the coating should be resist- 
ant to impact and to abrasion, the latter 
being the most important. The soft met- 
als, such as tin and zinc, do not stand 
up well against abrasion, but unless 
their adherence be very defective, they 
will stand impact well, on account of 
their malleability at ordinary tempera- 
tures. It would be desirable to obtain a 
coating which would be as good a pro- 
tection as zinc but tougher and harder. 
Aluminum is being used with some suc- 
cess and if the metal were cheaper it 
would become an interesting competitor 
of zinc. 

Different Behavior of Tin Plate and 
Galvanized Iron. 
But there is a more important feature 
of metallic coatings to be taken into con- 
sideration. This feature I shall intro- 
duce by the following example: If you 
make an incision in the surface of a 
sheet of tinplate and a similar one in a 
sheet of galvanized iron and expose the 
two sheets together to the same oxidiz- 
ing agencies, you will soon note a very 
great difference in the behavior of the 
two mutilations. The cut in the gal- 
vanized iron will rust very slightly or 
nut at all and the zinc at the edges will 
be oxidized, but the cut in the tinplate 
will not only show much more rapid and 
intense oxidation of the iron but the cor- 
rosion will extend beyond the edges of 
the cut. and in spite of the tin. A pin- 
hole in a galvanized sheet will not rust; 
a pinhole in a tinplate will spread out 
like a star. 

Metals in Contact. 
T must now call your attention to a 
few scientific principles which are all- 
important when considering metallic 



Gift, 



; 180r 



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TRAXSACTIOXS AMERICAN FOUXDRYMEX'S ASSOCIATION 



99 



coatings. In order to understand the 
reason for the different behavior of the 
galvanized iron and the tin-plate, it is 
necessary to thoroughly understand what 
takes place when two metals are in con- 
tact. For the purpose of the present dis- 
cussion we must consider four cases of 
metals in contact as follows : 

First — In the presence of electricity. 

Second — In the presence of heat. 

Third — In the presence of corrosive 
agents. 

Fourth — Apart from any exterior 
agency whatever. 

In the Presence of Electricity. 

As regards the first case, it is important 
to note that copper conducts electricity 
better than does iron, iron better than tin, 
tin better than lead, lead. better than zinc 
and zinc better than antimony. The 
metals first mentioned are negative to 
those which follow ; iron is negative in 
relation to zinc and zinc is positive in 
relation to iron. The conductivities of 
these metals are the reciprocals of their 
resistivities, in other words, the better 
conductivity of copper over iron is due 
to the smaller resistance which it op- 
poses to the passage of the electric cur- 
rent. Again, the better the metal con- 
ducts electricity the less capacity it has 
for storing it: this is the same as in the 
case of heat, the poorer the body as a 
conductor, the more difficult it will be 
to heat it, but the longer it will take to 
cool. The wooden handle of a silver tea- 
pot does not heat up as well or as rapidly 
as does the pot itself, but when the tea- 
pot is cooled the metal part cools quick- 
est and becomes colder than the handle. 
If, now, two metals, say iron and zinc, 
are put in contact and immersed in an 
electrically charged medium., the iron be- 
ing the better conductor will not absorb 
as much electricity as the zinc, and there 
will exist what is known as an electro- 
motive difference of potential, there will 
be a difference of electrical pressure be- 
tween the iron and the zinc in contact, 
and therefore a steady current of elec- 
tricity will flow from the zinc to the 
iron, and this current will be kept steady 
by the leakage which is directly propor- 
tional to the absorbing power. If no 
leakage were possible the potential of the 
two metals would reach the same level 



and they would be in electrostatic equili- 
brium equivalent to a closed circuit. 

An apt comparison to what takes place 
would be that of two water tanks of 
equal dimensions, connected at the bot- 
tom and at the top by open pipes, and 
one tank having a larger intake at the top 
than the other ; if both tanks are filled 
simultaneously by steady streams of 
w r ater, the tank with the larger intake 
will fill more rapidly and there will be 
a continual flow through the lower con- 
necting pipe from the tank with the larger 
intake to the tank with the smaller in- 
take to maintain the level. When the 
tanks are full they will be in equilibrium, 
and if they are turned upside down the 
outflow through the intake pipes will be 
proportionate to the previous inflow and 
the current will be reversed, passing from 
the tank with the smaller outflow to the 
tank with the large outflow in which the 
level is going down more rapidly. It is 
this operation of maintaining, or rather 
the effort to maintain the electrical level 
which produces the flow between metals 
of different conductivity when they are 
in contact and immersed in an electrically 
charged medium. The medium itself may 
be perfectly static, or at rest, but the 
flow from the iron to the copper will 
manifest itself as dynamic, or moving 
electricity ; nothing in nature, be it ma- 
terial or immaterial, can be manifested 
to our senses unless there be a motion, a 
difference, a relation. 

Electricity is always present on this 
planet, and everything is fairly impreg- 
nated with it, if, therefore, we bring two 
dissimilar metals into mutual contact we 
shall obtain a flow of electricity from one 
to the other, caused by an ineffectual ef- 
fort to equalize potentials, which will 
produce sensible galvanic effects. The 
contact need not be direct ; a suitable con- 
ducting connection, such as moist air, 
will act as an electrolyte and enable the 
action to take place, the space in be- 
tween constituting what is known as a 
field of force. Besides atmospheric and 
telluric electricity we are often called 
upon to take into consideration, in our 
engineering problems, the electricity arti- 
ficially produced for industrial and do- 
mestic purposes, the diffusion of which, 
or "stray currents" as they are called, 



100 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



will hasten the corrosion of water pipes 
and structural steel, even when they are 
embedded in concrete. 

The reverse of the order in which I 
have previously placed the metals in re- 
lation to their conductivities — i. e.. anti- 
mony, zinc, lead, tin, iron and copper, 
indicates the positive direction in which 
the current will flow from metals having 
the higher to those having the lower po- 
tentials ; it is known as an electromo- 
tive series. 

In the Presence of Heat. 

The second case is that of metals in 
contact exposed to heat. The electrical 
conductivity of substances will vary with 
temperature, that of metals decreasing 
with an increase of temperature. There 
are notable exceptions to any generaliza- 
tion which might be attempted that the 
conductivity is inversely proportional to 
the temperature, and one of these excep- 
tions happens to be iron. 

When two metals in contact are sub- 
iei ted to heat the voltaic or galvanic 
action of which I have spoken will be 
influenced either favorably or unfavor- 
ably because the thermo-electric series is 
different from the electro-motive series 
which I have given you. The thermo- 
electric series runs as follows : lead, tin, 
copper, zinc, iron and antimony. The 
order of these metals indicates the direc- 
tion in which the current tends to flow 
with an increase of temperature, this 
tendency may lie, and is in most cases, 
exhibited as. either a resistance or as an 
aid to the electromotive current; for in- 
stance, increase in temperature will re- 
duce the current from zinc to iron in a 
lesser degree than from antimony to iron. 
This principle has been used in the con- 
struction of electric pyrometers in which 
the variation in the temperature of a 
couple formed of dissimilar metals is 
recorded very sensitively at a distance 
from the source of heat, by means of a 
galvanometer. 

The galvanic effect between metals is. 
therefore, modified in a very complicated 
manner and to a considerable extent by 
the temperature at the point of con- 
tact. This galvanic action seems to be 
intimately related to the natural tendency 
towards chemical action exhibited by all 
substances in contact and to that chemi- 



cal affinity which exists to some degree 
or other between all kinds of matter. 
In the Presence of Corrosive Agents. 
The third case is that in which corro- 
sive agents are present which attack both 
of the metals. A decrease of electrical 
potential seems to aid chemical action 
and an increase of this potential opposes 
it. The metal towards which the flow 
of current is directed is, so to speak, 
over-saturated on. account of the persist- 
ence of effect which, when it refers to 
magnetism is called hysteresis, and its 
potential is greater than normal. The 
How of current from zinc to iron will 
over-saturate the iron and will prevent 
its decomposition, when it is exposed to 
corrosive influences, whereas the zinc 
which is under-saturated is in poor physi- 
cal condition to withstand chemical at- 
tacks. It will decompose into oxide and 
carbonate more rapidly than if it were 
out of contact with the iron. If only one 
of the metals is attacked by the corro- 
sive agents under normal conditions, 
there will lie no galvanic protection and 
this is why nickel-plating which is unaf- 
fected by ordinary atmospheric condi- 
tions is nothing more than a protective 
skin and if it is partially removed the 
exposed surface of the irons rust very 
readily. Copper-plating is no better, and 
if the iron is exposed the galvanic action 
is slightly unfavorable because the cop- 
per is in negative relation to the iron. 
Copper rolled over iron and then drawn, 
forms a good protection, but in this case 
the iron i^ nothing but a core. Lead 
would be a good coating metal if it were 
only harder and more readily attacked by 
acids. 

Apart From Any Outside Agents. 

The fourth and last case is that of 
metals in contact without any exterior 
agents being taken into account. Care- 
ful investigation has shown conclusively 
that if two metals are placed in close 
contact there will be a slow exchange of 
molecules, which will result in the metals 
alloying at their surface. If great pres- 
sure is applied during this exchange, the 
metals may be actually welded together. 
This action does not take place in a 
minute, nor even in a day or a month. It 
is very wonderful what pressure will do; 
certain salts in a finely powdered state 



TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 101 



have been compressed beyond a critical 
point where the cohesion became equal 
to that of the substance before it was 
pulverized and even transparency was re- 
covered. What enormous power must 
exist within the atom to bring about the 
same results by rapid and unimpressive 
reaction; such as the recovery of crys- 
tals by dissolving a pulverized substance 
and then evaporating it. 

This exchange of molecules between 
metals in contact is a simple case of dif- 
fusion. The diffusion of metals takes a 
great deal longer than that of liquids or 
gases because the internal friction is 
vastly greater; if the molecular cohesion 
is reduced by fusing the metals, the al- 
loying will take place as readily as when 
whisky and water are mixed to form the 
alloy, which is known as a "high-ball." 
If the metals could be brought to a state 
of vapor, the diffusion would be practi- 
cally instantaneous, and even if only one 
of the metals were in a state of vapor 
this should hasten the process to a con- 
siderable extent. I must ask you to take 
good note of this statement, because it 
has a very important bearing on the pro- 
cess and nature of dry galvanizing. 

The effect of pressure is to hasten the 
action, but diffusion will always take 
place between metals provided there is 
some kind of contact. According to this 
theory the metals of alloys should be- 
' come more thoroughly incorporated with 
time, and a zinc coating which has passed 
through the early stages of its existence 
without being destroyed should, like wine 
and love, improve with age; the two 
metals should gradually become alloyed 
at their surface of separation. If the 
old Ninivites or Egyptians had pro- 
duced galvanized work there would be 
people to worry over the lost art of al- 
loying iron and zinc just as others still 
persist in claiming that some useless art 
of hardening brass has been lost, al- 
though it has not even been proved as 
yet that it ever existed. 
Specifications For an Ideal Coating. 

On looking back at the four cases of 
metals in contact which I have discussed, 
you will readily see that all are closely 
related and that they must in all nor- 
mal cases be present at one and the same 



time. What then are the specifications 
for an ideal metallic coating for iron? 

First — It must be as far as possible 
from iron towards the positive end of 
the electromotive series and must ful- 
fill the same requirements in the thermo- 
electric series. 

Second — It must be affected by the 
same agents which corrode the iron. 

Third — It must present as large a sur- 
face as possible to the corroding agents. 

Fourth — It must be in very close con- 
tact with the iron. 

Zinc is, of all the commercial metals, 
the one which most closely fulfills the 
first and second requirements ; the third 
and fourth in regard to surface exposed 
and contact with the iron, are matters 
of process, and I shall, therefore, now 
proceed to describe the various processes 
which have been used to apply zinc to 
metal surfaces, but before doing so I 
want to point out that all these princi- 
ples which I have enumerated apply as 
well to the salts of the metals and that 
is undoubtedly one reason why red lead 
and zinc white give such good protection 
against corrosion. 

Cold Galvanizing. 

In the early years of the last century 
the process of electrolytic zincing, which 
is nowdays known as cold or electro-gal- 
vanizing, was first discovered, but until 
about 10 years ago the lack of suitable 
equipment prevented its commercial ap- 
plication. The articles to be treated by 
this process are first thoroughly cleaned 
of scale, rust and grease by an acid pick- 
le, sand-blasting, hot lye or by other 
means, singly or in combination, and are 
then placed as cathodes in a solution of 
some salt of zinc — usually the sulphate — 
in presence of zinc and which regenerate 
the solution, while a current of low volt- 
age is passed through the arrangement 
and deposits zinc from the solution upon 
the articles. Numerous factors must be 
taken into account; the composition and 
temperature of the bath; the voltage and 
density of the current; the quality, shape 
and position of the anodes, and many 
other points which are all of prime im- 
portance if the results are to escape first 
criticism and then corrosion. 

The surface of an electrically galvan- 
ized article is matt or frosted, provided 



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TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



the work has been properly done. It al- 
ways shows a few pores. If improperly 
done, or if the work was not perfectly 
clean before treatment it is either hon- 
eycombed with pin holes or spongy. 
Above a certain limit of thickness, below 
which the coating is worthless, first class 
electro-galvanizing is superior to hot- 
galvanizing and it is cheaper to produce 
where automatic machinery can be em- 
ployed, although less zinc is deposited 
than by a hot dip. This is no doubt due 
to the better contact between the zinc 
and iron. 

Hot Galvanizing. 

Sixty years ago the process of hot-gal- 
vanizing was introduced on a commercial 
scale. It consists in dipping the articles 
into a bath of molten spelter, with or 
without other metallic additions, at tem- 
peratures ranging from 750 to 900 de- 
grees Fahr. The articles must be first 
cleaned as for electrolytic work, but a 
slight falling short of perfection does 
not have such disastrous effects on the 
quality of the result. Very heavy pieces 
may be heated before dipping so as not to 
chill the bath. The coating is crystalline 
or amorphous and does not adhere as 
perfectly as does the electrolytic one. 
Properly treated sheet metal goods have 
an attractive spangled - appearance hut 
most articles look like castings and sharp 
edges are lost. Metallic chlorides are 
used as fluxes, they are expected to re- 
move the injurious salts of iron left by 
the pickling, hut it is a question if it is 
not another case like the introduction of 
rabbits in Australia, and if they them- 
selves are not the main cause of the de- 
cay which starts underneath the coating 
in hot-galvanizing work.* 

Dry Galvanizing. 

The latest process for applying a zinc 
coating, is the dry process, and I am go- 
ing to endeavor, not only to describe the 
process itself, hut to show you also how 
it fulfills the requirements which I have 
indicated, how it permits the extension 
of galvanizing to articles which have 
never been protected in this manner and 
how by divulging the mystery of the na- 
ture of zinc dust it permits us to specu- 



' The fumes eiven off in hot work are in- 
jurious to machinery ami in a manufacturing 
concern it is necessary to erect a separate 
building for this work. 



late along new lines in metallurgy which 
may lead to the discovery of some princi- 
ples of great industrial value. 

The process of dry galvanizing or 
Sherardizing metals was awarded a gold 
medal at the St. Louis exposition of 1904 
and the president's gold medal for 1903 
was presented to its discoverer by the 
British Society of Engineers. The in- 
ventor, Sherard Cowper-Coles, is one of 
the most eminent metallurgical engineers 
in Europe and is well known for his re- 
introduction on a commercial scale of the 
process of electric galvanizing, the regen- 
erating of electrolytes by the coke and 
zinc dust filter, the electrolytic spinning 
of copper into sheets, wire and other 
forms, and innumerable other invent'cms 
and improvements in connection with the 
electro-deposition of metals. 

The Practice of Dry Galvanizing. 

For the purpose of Sherardizing, the 
articles are placed, after cleaning, in a 
retort — usually a drum— and are covered 
with zinc dust, which is commonly called 
blue-powder, and is the flue-dust, and, 
therefore, a by-product of the zinc smelt- 
ing furnace known as the Belgian fur- 
nace. It contains as a rule from 75 to 
90 per cent of pure zinc; the supply of 
zinc-dust is ample at a price below that 
of spelter, and if the demand increases it 
can lie produced in any quantity that may 
lie required. A small amount of pou - 
dered charcoal is added to prevent oxida- 
tion of the zinc by the air inside the re- 
tort at the beginning of the operation, 
and the receptacle is closed and heated 
to a temperature about two hundred de- 
grees below the melting point of zinc. 
Ideal conditions would obtain if the air 
were exhausted from the drums. Where 
the size of the plant warrants the con- 
trol of the zinc-dust consumption to 
within so fine a margin, the drums might 
be filled witli some inert gas such as car- 
bonic dioxide which is supplied to soda 
fountains and other uses in steel bottles 
at a very low cost. It is, however, to be 
feared that if the temperature is allowed 
to go too high the carbonic dioxide 
might act as an oxidizer on some of the 
dust. 

By Sherardizing, a homogeneous de- 
posit of zinc is obtained, varying in thick- 
ness according to the length of time the 



TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 103 



article is allowed to remain in the re- 
tort, its lower portion being an alloy of 
zinc and iron or of zinc and copper, as 
the case may be. In the case of copper 
the alloy is a true and hard brass. The 
drum is occasionally turned a fraction of 
a revolution to insure an even coating 
where the articles are crowded together, 
and the heating may last from a few 
minutes to several hours and two or 
three drums can be used in connection 
with one furnace. 

A Sherardized surface resembles in 
general appearance an electrically coated 
surface. It is, however, of a soft silver- 
gray, more lustrous and metallic and, on 
that account, it is to most people, more 
pleasing to the eye, and it is distributed 
with great uniformity, which is not the 
case in hot galvanizing. Whereas in hot 
galvanizing the amount of zinc which is 
alloyed to the metal of the article is very 
small and most of the coating forms an 
exterior perishable skin, in Sherardizing 
the coating is thoroughly incorporated 
with the metal which it protects, forming 
an alloy having the appearance of pure 
zinc but much harder and more durable. 
It is on account of this thorough alloy- 
ing that the protection afforded by Sher- 
ardizing is so superior to that afforded 
by either hot or electric galvanizing. 
The zinc having penetrated the iron, the 
old surface cannot be recovered by either 
chemical or mechanical means. 

If an excessive amount of zinc is de- 
posited by Sherardizing, the outside sur- 
face is composed of zinc somewhat hard- 
ened by the presence of a small percent- 
age iron, and zinc-dust accumulates and 
clusters in a way which renders the sur- 
face rougher and much less attractive in 
appearance under magnification than it is 
to the naked eye. No special advantage 
is derived from the additional expense 
unless the conditions under which the 
articles are to be used are exceptionally 
severe. 

The process of Sherardizing is not con- 
fined to zincing; the dusts of antimony 
and of other metals can be used in a 
similar manner. The fact that zinc-dust, 
even at temperatures higher than its 
melting point, does not melt or cake, is 
of great value in Sherardizing, as 
it eliminates the danger of spoilt 
work from carelessness in hand- 



ling the temperature. Furthermore, zinc- 
dust containing as little as 35 per cent of 
pure metal can be used. The presence of 
the oxide is probably necessary, as it 
seems to play a part in the process. 
Some Anomalies of the Process. 
But why is it that zinc-dust acts in this 
peculiar manner, depositing zinc at a 
temperature several hundred degrees be- 
low its melting point, and why is it that 
the comparatively cold zinc alloys itself 
to the iron or other metal when the mol- 
ten zinc of the hot process fails to do so, 
or at best only does so in a cumbrous 
limited way? I can only answer these 
questions by giving you my own theory 
of the nature of zinc dust and of its 
action under the conditions of Sherard- 
izing. This theory is quite new to the 
very best of my knowledge and was not 
published by me until quite recently;* it 
is founded on observed facts but is not 
entirely empirical, because so far it has 
seemed to satisfy all the theoretical tests 
to which I have been able to put it and 
it answers a number of unexplained phen- 
omena which I shall mention later. 
The Nature of Zinc-Dust. 
The vapor of zinc which is given 
off at a temperature of 1,000 degrees 
Cent., or more, at the inception of 
distillation, comes into contact with 
the comparatively cold atmosphere of 
the flue, the sudden chill causes a 
rapid condensation of the vapor, so 
rapid indeed that it skips the liquid 
stage and drops in the shape of per- 
fectly spherical particles of which 
about 30,000 million can be crowded 
into a cube measuring one-sixteenth 
of an inch in every direction. This 
impalpable powder which, notwith- 
standing its high specific gravity — 
for it is only about 10 per cent light- 
er than zinc — can be blown about like 
lycopodium, is used mostly by paint 
manufacturers and is sold packed in 
barrels holding about 1,500 pounds. 
It is 10 or 15 per cent cheaper than 
virgin spelter at equal content of 
free zinc. It cannot be melted into 
slabs on account of its rapid oxida- 
tion at a very low temperature. 
The peculiar properties of zinc-dust 

*Electro Chemical and Metallurgical Industry, 
May, 1907. 



10+ TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



have been ascribed by some to the 
presence of cadmium, which being a 
more volatile metal is distilled first 
from the ore and condensed in the 
flues; one observer found quantities 
ranging from 0.283 to 0.794 per cent 
in flue dust after two hours of fur- 
nace operation. Others have claimed 
that these properties are due to the 
presence of zinc oxide or other im- 
purities. No plausible reasons for 
these theories have as yet been ad- 
vanced. 

Most of the zinc-dust is produced 
in Belgium or in Silesia, and a sam- 
ple which I have had analyzed 
showed the following composition: 

Metallic zinc 88.95 

Zinc oxide 6.88 

Lead 3.45 

Cadmium 0.62 

Sulphur 0.55 

Iron 0.04 

G. Williams, an English chemist.* 
has shown that zinc-dust takes up 
water and decomposes it and gives 
up its hydrogen on heating; he has 
also shown that it absorbs hydrogen 
at ordinary temperatures when sur- 
rounded by it in a moist condition, 
and that heated alone it yields 50 
times its volume of hydrogen, but 
when heated to redness with an equal 
weight of zinc hydroxide it gives off 
535 times its volume of hydrogen. All 
this may have some bearing on the 
antics of zinc-dust and on Sherard- 
izing, but as I am about to show it 
is unlikely and lacks confirmation, 
both theoretical and practical. 

It is my belief that these impuri- 
ties have little or nothing to do with 
the properties of zinc-dust and that 
the reasons should be sought for in 
its mode of production. 

If under similar conditions of rapid 
cooling we produce other solid bodies 
we get unstable and brittle results. 
If a bead of fused glass is dropped 
into water a "Ruperts' tear" is the 
result. As you know, a Ruperts' tear 
is very unstable and whereas for a 
drop of normal glass of similar di- 
mensions several good strokes of the 
hammer would be required to pulver- 
ize it, the Ruperts' drop can be shiv- 
ered to fragments by breaking off its 

* Chemical News, Vol. 52. 



tail with two fingers, or by scratch- 
ing the surface film where tension 
keeps the drop together. The dif- 
ference of energy required to effect 
the destruction of the normal drop 
and the Ruperts' drop is enormous. 

If we assume that zinc-dust is in 
this critical state we can explain al- 
most every one of the effects which 
have puzzled chemists during the past 
forty years. Douglas Carnegie* found 
that zinc-dust instantly reduced fer- 
ric to ferrous salt, and this even in 
neutral solutions (the italics are his); 
this action he states was consider- 
ably quicker than with granulated 
zinc in the presence of sulphuric acid. 
He was at first inclined to ascribe 
this wonderful efficiency to the oc- 
cluded hydrogen mentioned by Wil- 
liams, but further experiments, which 
I need not detail, showed that he was 
mistaken. Referring to another chem- 
ical operation in which zinc-dust act- 
ed with equal promptness, he writes: 
"Zinc-dust merely effects instaneous- 
ly the dechlorination which I found 
zinc foil required several hours to 
effect." 

It is so well known that zinc-dust 
has a great affinity for oxygen at a 
low temperature that it has been 
used for a long time in the dis- 
charge style of ' printing of cotton 
goods. The fabric is first dyed a 
plain color and it is then printed on 
with a discharge paste. The zinc 
c'.ust acts as a reducing agent at the 
temperature of the boiling water in 
which the cloth is dipped to effect 
the discharge. 

A fact that is undoubtedly respon- 
sible in a great measure for the mys- 
tery attaching to the action of zinc- 
dust is its readiness to oxidize. It 
is only when oxidation is put out of 
its power, as in the closed Sherard- 
izing drum, that heat will produce 
sufficient overstrain to cause the par- 
ticles to burst into vapor. This va- 
por so suddenly released will con- 
dense instantly on the coolest spaces 
it can find. In Sherardizing the cool- 
est spaces arc on the articles in the 



*Trans. Clicw. Soc., London, yr. 188S, p. 
46S. 



TR.1XSACTI0XS AMERICAN FOVXDRYMEX'S ASSOCIATION 105 



drum, and the drum itself being al- 
ways hotter does not receive any de- 
posit. One drum has already lasted 
two years without being coated. Zinc- 
dust appears to break down into va- 
por ' at about ISO to 200 degrees 
Cent., although it undoubtedly begins 
to disintegrate at a lower heat; as 
the pressure increases it takes a 
greater amount of heat to cause the 
breakdown; as the vapor condenses 
the pressure is relieved and the hot- 
ter particles of dust are vaporized 
and re-establish an equilibrium. In 
reference to this question of the vap- 
orization of zinc, it is a well-known 
fact that zinc will at ordinary tem- 
peratures affect a photographic plate. 
This has always been ascribed to 
zinc vapor which exhibits in that 
state great chemical activity. Radi- 
ology, the new science, is expected 
to bear the burden of all such ac- 
tions and I suppose I ought to say 
that the action of zinc on photo- 
graphic plates is due to the slow dis- 
integration of its atoms into energy 
and helium. 

In a small way it is a significant 
fact that zinc-dust is intensely exo- 
thermic in its reactions, which means 
that these reactions are accompanied 
by the production of heat. I could 
also mention the property first point- 
ed out by Schwarz, which zinc-dust 
has of combining violently with sul- 
phur by percussion. 

It has been known for some time 
that a cement made out of certain 
oils and zinc-dust possesses the use- 
ful property of becoming exceedingly 
firm and adhering closely to iron, 
steel and other metals, when heated 
to a temperature of ISO degrees Cent., 
or even less, if treated for a suf- 
ficient length of time. The theory of 
the nature of zinc-dust which I have 
given explains this hardening by the 
release of the zinc from its peculiar 
condition to form a solid without the 
formality of passing through the liq- 
uid stage. In the body of the ce- 
ment it is protected from oxidation 
and the zinc becomes mechanically 
continuous. It is an excellent com- 



position for calking cracks and crev- 
ices in metallic objects, for packing 
joints and for smoothing off the sur- 
face of castings. 

I think that I have given you a 
sufficient number of examples to 
show that zinc-dust is a substance in 
a very abnormal physical condition 
and if I have spent so much time in 
doing so, it is because I feel certain 
that by taking advantage of this ab- 
normal condition the metallurgical in- 
dustries will before long reap im- 
portant benefits. 

Zinc Vapor and Ferro-Zinc. 

I must tell you more about zinc 
vapor. This vapor is a gas just like 
air or any other gas and subject to 
the same physical laws, but as it is 
produced by the breakdown of zinc- 
dust particles at a very moderate tem- 
perature, it finds itself in the gaseous 
state at a point below its critical 
temperature and it will therefore 
readily assume the solid state by con- 
densation under its own pressure, 
confined as it is within a retort. 

When iron is pickled, hydrogen is 
given off on the surface and rises to 
the top of the vat. The pickle works 
its way into the metal and hydrogen 
is given off below the surface and 
remains occluded. This occlusion has 
very surprising results ; the surface of 
the iron is hardened and if it is to 
be drawn through a die or worked 
in any way, it is necessary to bake 
out the gas. Hydrogen has been long 
suspected of metallic proclivities; it 
is often classed as a metal. It is 
known to form an alloy with palla- 
dium and it is supposed to alloy it- 
self to the iron to produce the hard 
skin of which I have spoken. Zinc 
vapor acts in the same way in Sher- 
ardizing, but it forms an alloy all the 
more readily because in its normal 
condition it is itself a metal as we 
generally understand that rather ar- 
bitrary term. 

Being a gas, the zinc vapor can 
force itself into the pores of the 
metal and form a deposit to a depth 
which will increase with the dura- 
tion of the treatment. A small piece 



106 



TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



can be alloyed throughout. An alloy 
of zinc and iron produced by fusion 
would be a sorry article when it came 
to be tested; "zinc-eisen," as it is 
called, is zinc ruined by the addition 
of a quantity of iron, which renders 
it brittle and worthless. By alloying 
with vapor at a low temperature the 
qualities of the metal cannot be in- 
jured, but they may be greatly im- 
proved by the zinc forming an inter- 
molecular binding, which fills spaces 
which would otherwise allow motions 
of the particles under stress which 
might injure their cohesion; the va- 
por deposit should increase tough- 
ness and it is quite possible that this 
theory may have some bearing upon 
the general subject of the nature of 
alloys. 

By using carbon as a condenser for 
free zinc vapor, out of contact with 
the dust, I have obtained a perfect 
zinc dew. I used a common arc lamp 
carbon and the drops on the top were 
large and reduced in size down to 
microscopical proportions on the 
edges. Here and there on the in- 
side were traces of zinc, showing that 
the gas had penetrated the mass. The 
zinc vapor had not alloyed to the 
carbon, the specific heats being wide 
apart, whereas I have observed that 
the closer the specific heats of the 
zinc and the material to be coated at 
their working temperatures, the more 
quickly and firmly would they com- 
bine. It is no doubt on this account 
that copper Sherardizes so much 
more rapidly than does iron. 

Improvements in Sherardizing will 
undoubtedly be founded on the intelli- 
gent control of the temperature, but to 
this end temperature readings will 
have to be taken inside the retort and 
not in the furnace as heretofore. 

Working with gas alone and under 
the special conditions necessitated by 
the peculiar circumstances of the ex- 
periments, I was able to obtain quite a 
variety of deposits. Rapid cooling 
will cause (lie zinc to condense as 
crystals the adherence of which to the 
iron is, however, inversely proportion- 
al to their size. Normal cooling would 



seem to yield in all cases a fine glossy 
surface of what can be appropriately 
termed ferro-zinc. 

Examining this 1 ferro-zinc under 
about 400 diameters of enlargement it 
exhibits the structure of the original 
metal. A piece of mild steel which 
had been thoroughly pickled and which 
had been treated by vapor only, and 
was, therefore, free from any exterior 
zinc coating, such as would have con- 
cealed the alloy if operated on in con- 
tact with the dust, exhibited the usual 
structure of an etched mild steel. This 
ferro-zinc appears to be harder than 
the original iron and its rust-proof 
qualities are the true secret of the ex- 
ceptional efficiency of Sherardizing. 

The Creece test with sulphate of 
copper is not a fair test for Sherardiz- 
ing. it is almost without significance 
for the following reasons: The outer 
coating of the slightly oxidized zinc 
particles resists the text better than 
does the brighter hot coating or the 
porous electrolytic one, but the alloy, 
obtained by vapor treatment alone, 
and which is present in all Sherardiz- 
ing, readily takes the copper just as 
the iron itself would, and yet it will 
resist corrosion perfectly. The copper 
will deposit without destroying the 
zinc and the test is, therefore, worth- 
less. The only way to test Sherardiz- 
ing is to put it into service. 

The alloy known as nickel steel does 
not rust easily and yet in a nickel 
plated article if the nickeling is partly 
removed the iron will be corroded. 
This shows that we must not expect 
contact theories to adapt themselves to 
perfection to metals in solution, and to 
alloys. The alloy of nickel and iron re- 
sists corrosion and in my opinion it is 
a parallel case to that of ferro-zinc. 

The Romans to make their brass, 
which they called "Orichalcum," threw 
cadmia, (oxide of zinc) on highly 
heated copper. The more recent cal- 
amine brass, process which was in use 
until about one hundred years ago, 
consisted in heating calamine (zinc 
■ silicate), granulated copper and coke — 
dust in crucibles, the fusion and alloy- 
ing taking place at a temperature con- 



TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 107 



siderably lower than the melting point 
of copper. I thought these two points 
of history might interest you by com- 
parison and as aids to the digestion 
of the most recent developments. 
The Theory of Dry Galvanizing. 

Let us enter the Sherardizing retort 
and endeavor to find out what takes 
place. Which guess will offer the 
most plausible explanation? It is an 
established fact that in Sherardizing 
the presence of zinc oxide is neces- 
sary. We might suppose, therefore, 
that a molecule of oxide is reduced by 
voltaic action when it comes into con- 
tact with the iron; the zinc attaches 
itself to the iron which acts' therefore, 
as a cathode in electrolysis, and the 
oxygen travels in the opposite direction, 
combines with a free molecule of zinc 
to form a molecule of oxide, and goes 
through the same performance as be- 
fore. 

I have excellent reasons, which I 
must keep for later publication, for 
believing that this hypothesis is pret- 
ty close to the truth if not the true 
explanation of the action in dry gal- 
vanizing. 

The outer coating is composed of 
reduced zinc in granular form and the 
silver gray appearance may be due to 
slight oxidation of the surface. 

Whatever the true explanation may 
be it is of little immediate interest to 
"practical" men, but it is of great in- 
terest to scientists who are expected 
to continue furnishing their abstract 
facts to serve as souls to the concrete 
bodies created by inventors. The in- 
ventors, while claiming all the credit, 
usually sell or lose most of it to men 
who put these inventions into practi- 
cal use. He laughs best who laughs 
last, and by the time the invention has 
become an industry the poor scientist 
has been entirely forgotten, — except to 
be occasionally dubbed a theorician, a 
dreamer, a simple soul, a mild and 
childlike, — for of such is the kingdom 
of heaven. 

The Efficiency of Dry Galvanizing. 

The efficiency of dry galvanizing, 
which has been proved by thorough 
testing both in England and Germany, 



is' due to its fulfilling the conditions 
which I have set forth in the early 
part of this paper. 

Considered merely as a covering, it 
fits as closely as does an electrically 
deposited coating and it is impenetra- 
ble because free from pores or cracks. 

As a mechanical protection it resists 
both abrasion and impact better than 
hot or cold work because of the qual- 
ities' of the ferro-zinc alloy. Zinc itself 
is superior to both tin and lead in 
ductility and tenacity. 

Considered in relation to contact ef- 
fects the zinc distilled as vapor and 
alloyed to the iron is absolutely pure 
and the span between it and the iron 
in the electromotive series is, there- 
fore, extended as compared with a 
zinc containing a percentage of impur- 
ities. Its contact with the iron in the 
body of the alloy is as perfect as is 
possible. In relation to corroding 
agents its granular structure offers a 
maximum surface for them to decom- 
pose and, therefore, increases the ratio 
in which the coating acts by its own 
decomposition as a protection to the 
iron. 
Commercial Scope of Dry Galvanizing. 

It is a noteworthy fact that while 
many articles have appeared in techni- 
cal and scientific journals about Sher- 
ardizing, not one word of criticism or 
denial of its claims has' as yet been 
offered. I have been looking for seri- 
ous criticism for some time past but 
when I have found doubters I have 
only succeeded in making new con- 
verts. The process has always ap- 
pealed to scientific men because they 
are in position to appreciate the solid 
scientific foundations of its claims. 

The new process has not entered the 
field as a competitor to galvanizing 
alone: in a great many instances it 
can take the place of coppering, of 
nickel-plating and of tinning, where 
the articles are not to be used for the 
preparation or handling of foodstuffs. 
To these I should add the large 
amount of copper and brass articles, 
from tubing to typewriter and sewing 
machine parts which are now nickel- 
plated. An interesting point in rela- 



103 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



tion to the various methods of protect- 
ing metals is the price of the metals 
themselves. Nickel is 7u times, tin 
and aluminum 7 times, copper 4Vg times 
and antimony 3 r 4 times as high in 
price as spelter, and at equal efficiency 
against corrosion the lightest coating 
is one of zinc as applied by dry-gal- 
vanizing. 

Analyzing the various items which 
go to make up the cost of Sherardiz- 
ing, we find that in every instance 
there is a saving either over the hot 
process or over the electric process. In 
most cases the saving is over both of 
the older processes. 

Initial Expense. 
A plant for Sherardizing is less ex- 
pensive than a hot plant and very 
much less so than an electric plant. 
Every part of it is of a simple nature 
and calls for neither feat of engineer- 
ing nor for the solution of any out-of- 
the-way problems. It is very much 
like a plant for close annealing, and 
whereas the depreciation on a hot 
plant is usually taken at 50 per cent 
per annum, the depreciation on a 
Sherardizing plant would not exceed 
10 per cent, which is the depreciation 
commonly figured on an electrolytic 
plant. The drums are not made of 
perishable hard rubber or wood as are 
those for electrolytic galvanizing. The 
process can lie carried on in the main 
manufacturing building, and the pick- 
ling done in the cheapest kind of an 
outhouse. 

The Saving in Cost of Zinc. 
For an equal thickness of coating, 
the zinc actually deposited is about the 
same in value whether derived from 
dust or from spelter slabs. It is less 
than the anodes used in electrolytic 
work which have to be cast specially 
and are very often of odd or compli- 
cated form. Even less zinc is re- 
quired than in the electric process be- 
cause an equal thickness is more ef- 
fective and because the distribution is 
fully as even. In Sheradizing there is 
nothing to throw away, but sufficient 
dust (from 1 to 5 per cent) is added 
from time to time to replace that of 
the weight of the articles coated 



which has been used. There is no 
equivalent to the unsatisfactory results 
due to using spelter recovered from 
dross and therefore contaminated by 
the presence of iron. 

In electro-deposition an unobstructed 
path is required between the anode and 
the object, for, the dissociated ions of 
the salts in solution to travel. If any 
part is hidden or recessed no deposit 
is made and the parts furthest from 
the anodes have the lightest coating. 
In addition to this it must be under- 
stood that the anodes are not entirely 
used up and part of them is lost at 
the bottom of the tank, and as eaten- 
out remnants they cannot be used to 
the vanishing point. 

It is hardly necessary to point out 
the enormous saving in the quantity 
of zinc used as compared with the 
hot process. Hot galvanized articles 
have, as a r.ule, a much thicker coat- 
ing than is necessary because most of 
them cannot be conveniently wiped 
like wire or band iron. In Sherardiz- 
ing all the zinc is consumed and the 
thickness of deposit is regulated just 
as readily as in the electric process. In 
the hot process a large percentage of 
spelter is converted into dross and 
skimmings, and while much of it is re- 
covered, the net loss cuts quite a fig- 
ure on the cost sheet. 

The Saving in Labor. 

Sherardizing is like annealing in that 
it requires but a small amount of la- 
bor, and that unskilled, placed under 
proper superintendence. A drum 
holding one or more tons of articles 
can be left to itself for half an hour 
or more subject to an occasional turn; 
in the meantime another drum is be- 
ing prepared for Sherardizing while 
the first will be cooling. Suitable par- 
titions will allow of several classes of 
small articles being Sherardized in one 
drum without mixing. 

Hot galvanizing requires constant 
attention and handling, which can 
seldom be done by one man even with 
the aid of overhead trolleys and sim- 
ilar fixtures. It is not a mechanical or 
automatic process, but one of hard 
manual labor, and the regulation of 



TRANSACTIONS AMERICAN FOVNDRYMEN'S ASSOCIATION 109 



temperature and methods of dipping 
require the attention of an experienced 
galvanizer. 

As a leading authority on hot work 
has written: "Considerable skill is re- 
quired to bring a piece of work out 
of the metal and cool it so that the 
surface will be smooth, free from blis- 
ters and with no lumps of surplus 
metal attached." 

For the electric process at least one 
man possessing some knowledge of 
electricity and of all the whims of 
electrolytics is needed. In electro- 
deposition irregular shapes — excepting 
in the case of very small articles — re- 
quire regular shaped anodes, but in 
Sherardizing the dust, every particle 
of which may be considered as a min- 
ute anode in itself, is used just as it 
comes from the refiners for any size 
or shape of article. 

By combining the advantages of 
both the old processes, Sherardizing en- 
ables a manufacturer to galvanize with 
one plant only, articles which have hith- 
erto been divided between the two 
processes, the small ones being elec- 
tro-galvanized and the large ones 
dipped. Less care is needed in clean- 
ing the articles to be Sherardized, and 
oil or grease, far from being objection- 
able, are helpful to the process, be- 
cause their volatile hydrocarbons help 
to prevent oxidation of the dust; the 
addition of grease or vaseline has in- 
deed been found to be of some advan- 
tage in many cases. Furthermore, the 
articles can be put into the drums wet, 
as they come from the washing tank. 
The labor of recutting threads is 
eliminated. Bolts, screws and nuts 
can be put in the drum just as they are 
delivered from the machines, covered 
with oil or cutting compound. 

With small installations the process 
can be worked intermittently. The 
low cost of the plant warrants a man- 
ufacturer in running a drum two or 
three days a week instead of sending ■ 
his work out. thereby saving time, 
freight and jobbers' profits. The tem- 
perature required is so low that it 
takes very little time to start the fur- 
nace and where gas is used this ele- 



ment of time may be almost disre- 
garded. This' low temperature also 
suggests using the waste gases of an- 
nealing and other furnaces, and in 
many cases it will be found economical 
to place a whole day's production in 
the retort and leave it in overnight 
with the night watchman to keep his 
eye on the pyrometer. There is no 
labor for skimming and drossing; no 
pots to scrape at unexpected times, nor 
furnaces to destroy and rebuild at all 
too frequent intervals. 

The Saving in Fuel and Power. 

The plainest fact about hot galvan- 
izing is its thermal inefficiency. The 
pot must be kept going day and night, 
whether in use or not, and even dur- 
ing its operation most of the heat is 
lost by radiation and by having to 
bring the articles to the temperature of 
the bath. On the other hand, power is 
seldom an item of any consequence, 
whereas in electrolytic work the 
amount of current consumed is quite 
large, for a deposit which is meant for 
something more than exhibition pur- 
poses or to be buried out of sight and 
forgotten. This is seldom appreciated 
because electricity is unobtrusive in 
its action; the cost of electro-galvan- 
izing thin sheets is prohibitive on ac- 
count of the amount of current con- 
sumed. In Sherardizing the heat is 
very low and is kept in by a lining of 
refractory material; the articles do 
not have to reach the temperature of 
the zinc dust and the apparatus is al- 
ways ready for work on short notice. 
The temperature does not have to be 
varied to suit the different sizes and 
classes of articles to be coated and as 
I have suggested, waste gases can be 
used under many circumstances. 
Other Factors of Economy. 

With the new process, less acid is 
used than in the electrolytic process 
because the cleaning does not have to 
be so thorough. The vapor works its 
way under specks of dirt and bare 
spots cannot exist. No flux of any 
kind is needed as in hot galvanizing, 
and there are no comparatively high- 
priced electrical supplies to be bought. 

There is no danger whatever from 



110 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 



explosions, no broken castings nor dis- 
torted iron work to replace, and the 
temper of the finest steel blades and 
of steel springs is in no way injured by 
the low temperature used. This may 
at first seem strange and will not be 
perfectly clear until we know some- 
thing more about the temperatures ex- 
isting and the reactions taking place 
in the retort. 

Various Applications of Dry Galvaniz- 
ing. 

Sherardizing will not full an uncalked 
seam and act as a solder, this is its one- 
limitation but it has a great variety of 
new applications to make up for it. Fly 
screening can be galvanized and the 
business parts of agricultural imple- 
ments such as mower and harrow teeth 
can receive adequate protection at a 
low cost without impairing their qual- 
ities. 

Flashing a surface electrically to dis- 
cover flaws has been in use for some 
years and Sherardizing will render the 
same service; it is, in fact, being used 
at the present time for this very pur- 
pose for boiler tubes. However, while 
electric flashing is worthless against 
corrosion, a flashing with zinc dust or 
vapor is very effective as a rust pre- 
ventive, and of particular service for 
articles which are to be shipped across 
the ocean. 

Within reasonable limits innumera- 
ble machined articles, tools, locomo- 
tive and engine parts can be flashed 
with zinc and be effectively protected 
against rust under the conditions of 
their operation, whereas at present 
they must be periodically cleaned at 
the expense of their appearance and of 
the accuracy of their fit. Articles 
such as wire, tubes, etc., either flashed 
or coated with a heavy deposit can be 
drawn out, the coating drawing out 
with the material itself. 

A brilliant and permanent polish 
which can hardly be distinguished 
from nickel-plating, but bluer and 
more like silvrr. and a better reflector 
of light, can be given to Sherardized 
articles by means of the usual burn- 
ishing tools and machines, but unlike 
nickel-plating it is absolutely rust- 



proof. This polish is not temporary 
like that of electro-galvanizing, and it 
is hard and durable if worked down, as 
it should be, t > > the ferro-zinc. The rea- 
son that it does not whiten by corro- 
sion, as might naturally be expected, is 
because the surface has flowed to an 
inpervious film and the iron is shielded 
from any contact effects. In this con- 
nection it should be remembered that 
highly polished steel is relatively rust- 
proof. If, however, nickel-plating is 
preferred a light Sherardizing before 
plating, instead of coppering, will en- 
sure very thorough adherence of the 
nickel to the ferro-zinc and superior 
rust-proof qualities will be obtained. It 
has been shown that it is very difficult 
to volatilize zinc from alloys where 
there is any nickel present.* 

Sherardized aluminum can be elec- 
tro-plated and the objectionable soft 
surface be overcome, not to mention 
the finish and appearance. 

Sherardizing has been found to pro- 
tect silver from sulphated hydrogen 
which blackens it; it can be applied 
very lightly before polishing without 
altering the color. When aluminum 
has been Sherardized it can be readily 
soldered; this is expected to do away 
with the very unsatisfactory riveting 
of articles made from aluminum sheets. 
The latest application is for inlaying 
or damascening and this art is being 
carried out in England on a commer- 
cial scale. A variety of colors can be 
obtained by using different dusts and 
by varying the time, thereby obtain- 
ing alloys of different tints. The de- 
signs shade off in a pleasing manner 
beyond the edges of the stopping-off 
material which acts as a stencil in set- 
ting graphical limits to the action of 
the dusts and vapors. 

It is very seldom that in the his- 
tory of invention we find an improved 
process which corrects so many de- 
fects', removes so many limitations oi 
the processes in use and creates so 
many new and novel applications as 
does dry-galvanizing. 

* See A. R. TTaslam in Chcm. News, Vol. 51. 



SCIENCE APPLIED TO THE BRASS 
INDUSTRY 

By Andrew M. Fairlie, Copper Hill, Tenn. 



For the sake of progress in the 
brass industry, as well as for the ad- 
vancement of science, it is highly de- 
sirable that the brass and scientific 
men learn to know each other better. 
Science is not nearly so formidable as 
many believe. She should be respect- 
ed, it is true, but not treated with awe; 
for the benefits she has bestowed, she 
should be admired, not feared and 
shunned; and while she continues to 
promise aid, economically lightening 
the labors of men, improving the qual- 
ity of products and the efficiency of 
processes, she should be cherished, not 
ignored, maligned not abused. 

Science, it must be admitted, is a 
forbidding word. Yet it need not be. 
As indicated by its derivation, science 
is' nothing more nor less terrible than 
knowledge. More specifically, it is 
the knowledge of nature's laws. An 
incident that occurred in the course of 
this day's work will illustrate at once 
the meaning of science, and its value 
to the brass industry. Mr. X. was 
superintending the manufacture of a 
new metal, an alloy of nickel and lead. 
He weighed the metals himself, and 
was particular that the percentages 
should remain exactly as' planned. He 
was out of the foundry when the lead 
was added, but stepped in just as the 
men were skimming, and as he did 
so, saw a heavy lump fall from the 
crucible to the floor. 

"What's that?" asked X. suspiciously. 

"Slag from the coke," was the reply, 
and this statement was corroborated 
by a fellow workman. 

Not content, X plunged the lump 
into water to cool it, scratched the sur- 
face with a file, and saw that the lump 
was not slag, but metal. Application 
of the magnet indicated that the metal 
was either nickel or iron, and a simple 
chemical test excluded the latter, so 



that the deduction was plain. The 
men chilled the nickel by adding the 
lead too fast, then skimmed off the 
frozen nickel, which had come to the 
surface of the lead, and so, entirely 
ignorant of this fact, spoiled their 
work. In this case only very ele- 
mentary science, or knowledge, if you 
will, was required to detect the error 
and apply the remedy — a new casting. 

Contemplating the help that science 
has already given the brass maker, ana- 
lytical chemistry at once claims our 
attention. This branch of chemistry 
detects injurious impurities in the com- 
mercial metals from which brass' is 
made; it locates and measures the 
losses in the business; by pointing out 
the sources of inaccuracy, it standard- 
izes the mixtures of a casting shop; 
it shows the exact composition of any 
metal submitted for reproduction; by 
selecting the good and bad qualities of 
molding sands it improves the quality 
of sand castings; it distinguishes good 
coal and coke from poor, and in many 
ways\ discovers the cause of trouble. 

Metallurgy, in its turn, has been of 
serviceV The methods of recovering 
metal ftom scrap have been improved. 
The cause of porosity in castings has 
been found, and the soundest castings 
are now possible by the use of de- 
oxidizers, such as silicon, phosphorus, 
aluminum or. magnesium. The oxida- 
tion of metals\in the foundry has been 
diminished by. keeping the molten 
metal surrounde^d as much as possible 
by reducing gases, both while melting 
and while pouring. The pernicious 
effect of the iron stirrer for mixing al- 
loys has been demonstrated, and one 
of graphite substituted. 

Physics has furnished the conduc- 
tivity bridge and the pyrometer. Since 
extremely small proportions of certain 
impurities in copper have a powerful 



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112 TRANSACTIONS AMERICAN FOUNDRYMEN'S A: 014 634 178 4 



effect in depressing the electrical con- 
ductivity, the former has been adopted 
as' a quick and accurate means of test- 
ing the purity of refined copper. The 
pyrometer, by controlling the temper- 
ature, tends to render furnace pro- 
cesses more exact. The microscope, 
extending its researches to the exam- 
ination of the non-ferrous metals, has 
been directed upon polished and etched 
sections, of copper, brass and bronze, 
and has revealed the varying structures 
resulting from different degrees of heat 
in melting and pouring, as well as from 
forging, rolling, and other mechanical 
pri icesses 

In the electro-plating industry the. 
value of circulating the electrolite, 
either by rotating an electrode or* 
otherwise, has been recognized and 
the principle applied. 

But it is not possible, nor, indeed, 
is it necessary, to enumerate within 
the limits of an association paper all 
of the scientific discoveries and inven- 
tions adopted in practice by the brass 
industry since the days when, eighty 
years ago, sheet brass was made in 
Waterbury, Conn., by alternately pass- 
ing the ingot between heavy steel rolls 
and annealing in the flames of a 
chestnut wood fire. So much for the 
past and present — what is the outlook 
for the future? Completeness applied 
to the future is. of course, out of the 
question, and one must be content with 
a study of the signs of the times. 
Even thus the limitations of time and 
space serve an injunction against com- 
pleteness, and we can consider here 
only a few of the problems which con- 
front this generation. 

We had in mind just now the elec- 
tro-plating industry. The electro-plat- 
ing shop needs the chemist and metal- 
lurgist more, perhaps, than any other 
branch of the non-ferrous metal in- 
dustry. An examination of the inquiry 
columns of the trade papers demon- 
strates that rule-of-thumb methods in 
the plating room do not meet the re- 
quirements. The trouble experienced 
by the "platers in controlling their so- 
lutions and costs and the quality of 
their work is simply evidence that the 



electro-plating shop ought to be, and 
must become an electro-chemical and 
metallurgical laboratorj r on a commer- 
cial scale; that the handful of this, 
the pinch of that, and the bucketful of 
the other — yes, even the dram and 
ounce and gallon — must give place to 
the gram and the liter; in short, that 
science must foster an industry that 
was born of science. It is too much 
to say that science is now prepared to 
solve off-hand any electro-plating pro- 
Idem that might be presented. Pro- 
blems in practice require scientific in- 
vestigation, and as electro-plating pro- 
blems have been neglected, much 
painstaking work will be required for 
their solution. Let us see what prob- 
ability of success is offered to stimu- 
late efforts in this direction. 

Ideally, the metal dissolved from an 
anode showed equal the metal depos- 
ited on the cathode, the bath remain- 
ing unchanged. Practically, this de- 
sideratum is today seldom achieved. 
Impurities in the anode dissolve in the 
bath, polluting it. and at the same time 
metal is deposited on the cathode more 
rapidly than it is dissolved from the 
anode. The excess is derived from the 
bath, with consequent variation in com- 
position. Furthermore, certain impuri- 
ties, insoluble in the electrolyte, either 
form a coating on the anode, partially 
insulating it, or, falling off. foul the 
bath; consequently the electrolyte has 
to be regenerated or renewed from 
time to time. Such obstacles' should 
not be regarded as insurmountable. 
On the contrary, experience shows that 
patient application of scientific princi- 
ples will overcome such difficulties. 
For example, several years ago Dr. 
N. S. Keith was confronted with a pro- 
blem in the electrolytic refining of lead 
base bullion.* His solution of lead 
acetate and lead nitrate became de 
posed, with the formation of insoluble 
salts which interfered with the d< : 
tion. The problem was finally solved 
by substituting for the original bath 
an electrolyte composed of lead sul- 
phate dissolved in sodic acetate. Dr. 
Keith avers that the integrity of this 



'Electrical Industry, June, 1903, p. 345. 



014 634 178 



Conservation Resources 
Lig-Free® Type I 
Pb 8.5. Buffered 



LIBRARY OF CONGRESS 



014 634 178 



Conservation Resources 



